Rich Freeman, mused, then expounded: > On Fri, Jun 21, 2013 at 3:31 AM, Duncan <1i5t5.dun...@cox.net> wrote: > > > The single down side to raid1 as opposed to raid5/6 is the loss of the > > extra space made available by the data striping, 3*single-device-space in > > the case of 5-way raid6 (or 4-way raid5) vs. 1*single-device-space in the > > case of raid1. Otherwise, no contest, hands down, raid1 over raid6. > > This is a HUGE downside. The only downside to raid1 over not having > raid at all is that your disk space cost doubles. raid5/6 is > considerably cheaper in that regard. In a 5-disk raid5 the cost of > redundancy is only 25% more, vs a 100% additional cost for raid1. To > accomplish the same space as a 5-disk raid5 you'd need 8 disks. Sure, > read performance would be vastly superior, but if you're going to > spend $300 more on hard drives and whatever it takes to get so many > SATA ports on your system you could instead add an extra 32GB of RAM > or put your OS on a mirrored SSD. I suspect that both of those > options on a typical workload are going to make a far bigger > improvement in performance. >
However, the incidence of failure is less with RAID1 than RAID5/6. As the number of devices increases, the failure rate increases. Indeed, the performance and total space can outweigh the increase in device failure. However, more devices - especially more devices that have motrs and bearings, takes more power, generates more heat, and increases the need for more backups to avert an increase in failures. Bob -- -
